Current mobile networks are based on an architecture where a core network (CN) is separated from a radio access network (RAN). The CN is further separated between a user plane (UP) and a control plane (CP), denoted CN UP and CN CP, respectively. For instance, in the case of Long Term Evolution/Evolved Packet Core (LTE/EPC) mobile networks, the RAN comprises eNodeBs (or eNBs), which act as base stations, BS, the CN CP comprises a Mobility Management Entity (MME), while the CN UP comprises a Serving Gateway (SGW) and a Packet Data Network Gateway (PGW). FIG. 1 illustrates this conventional architecture. It is noted that other entities may also be included. For instance, the CN CP may comprise also other entities (not illustrated), e.g. a Home Subscriber Server (HSS) and a Policy and Charging Rules Function (PCRF).
CN functionality is commonly deployed at a centralized location and is hence separated from RAN functionality that needs to be distributed at the base station (BS) sites. The CN control plane functionality comprises e.g. termination of non-access stratum (NAS) signaling with wireless devices and handling the associated signaling procedures, and functions such as setting up and updating of the user plane path for a user equipment's (UE's) data traffic. Separation of UP and CP in the CN helps to independently scale functions that require different types of implementations, and also allows operators to integrate equipment from different vendors. Such a split between RAN and CN, as well as the separation between UP and CP, simplifies network operations and has served operators well in providing public mobile broadband services.
The range of services provided by mobile networks is extending into other use cases, such as industrial applications. These non-traditional usage scenarios have been in the focus in the definition of the next generation of mobile network technologies, commonly referred to as 5G. New use cases comprise, for instance, industry automation use cases where field devices such as manufacturing robots, sensors or actuators are connected over mobile networks to a central controller, where the mobile network provides highly reliable and extremely low delay communications services.
In such a local network, separate entities for RAN (entities such as BS), CN UP and CN CP would be too complex and expensive to operate. Further, separate entities increase the risk of failure and also incur additional delays.
Collocating BS, CN UP and CN CP functionality in a common access node (AN) platform is possible, but for efficient handling of mobility between multiple such common AN platforms, additional functionality is needed. During mobility, a wireless device may be handed over from one common AN platform to another common AN platform. In case the CN CP functionality remains served by the old common AN platform, the system would need to rely on both the old common AN platform and the new common AN platform for operation. This is sub-optimal from a reliability point of view: it is preferable if the system relies on a single common AN platform only, as that reduces the number of failure points.
Another possibility is to re-locate the CN CP functionality to the new common AN platform after mobility, which increases reliability as the wireless device would not be dependent on a second common AN platform for CN CP functionality. The wireless device may move from the service area of a first common AN platform to the service area of a second common AN platform and then to a third common AN platform. As the wireless device moves, the corresponding control plane context of the wireless device is relocated. This is the solution e.g., in case of MME relocation during UE mobility with pool area change. For industrial applications, a solution could be to collocate the control plane functionality with the BS in a combined AN platform to achieve simpler operation and higher reliability. In such solution, handovers between base stations also imply context transfer for the CP.
However, CN CP relocation procedures from one AN platform to another imply a significant signaling overhead. According to existing system procedures, a relocation of the CN CP would need to be signaled separately to the UE, for which the assignment of a new globally unique temporary identifier (GUTI) is needed, and to the HSS to update the UE location. Such extra signaling loads the mobile network.
Further, a relocation of the CN CP might also be needed during a service request procedure. Such relocation is not possible today with the service request procedure as defined in the specifications, and extending the service request procedure for this relocation may make the procedure slower, which is a disadvantage as the service request is a time-critical action wherein the delay of the idle state to connected state transition needs to be kept low.